1. Field of the Invention
This invention generally relates to the management of the nuclear fuel cycle for the purpose of decreasing the probability of proliferation of nuclear fuel. More specifically, it relates to a process for recycling protactinium-231 to enhance the utilization of uranium-232 in nuclear fuel for the purpose of making nuclear fuel more resistant to proliferation. The process can be used in light water reactors, heavy water reactors, high temperature gas cooled reactors, and fast breeder reactors.
2. Prior Art
The deterrent effect of high energy gamma rays associated with uranium-232 has long been recognized. The deterrence is caused both by the higher radiation emitted by uranium-232 and by the heat produced by high concentrations of this isotope of uranium. This heating effect is similar to the deterrent effect of heat produced by the addition of plutonium-238 to plutonium fuel as has recently been proposed and reported in an article entitled, "AGNS Proposes Proliferation Resistant Fuel Cycle" published in the trade journal Nuclear Industry in September of 1978, and which is hereby incorporated by reference. This article reports that, in the minimim plutonium mass required for a weapon, a concentration of 5% plutonium-238 would produce a surface temperature of about 875.degree. C., thus posing difficult problems in accumulating and handling the critical mass of plutonium which could be used in the illicit manufacture of nuclear weapons.
U.S. Pat. No. 3,714,322 to Bell teaches a method for preparing high purity uranium-233. The method includes permitting the decay of protactinium-232 to uranium-232. However, Bell does not relate to a process for the production of uranium-232 for mixture with uranium fuel to make the fuel more resistant to proliferation. In addition, Bell discloses a process utilizing protactinium-232 rather than protactinium-231 as used in this invention. U.S. Pat. No. 2,900,228 to Seaborg et al relates to the production of uranium-233. As a step in the process of producing uranium-233, this reference discloses the utilization of uranium-233 and protactinium-233. However, this reference does not teach the separation of protactinium nor does it teach the conversion of the protactinium into uranium-232. U.S. Pat. No. 3,208,912 to Jaye et al, which is hereby incorporated by reference, teaches the use of thorium and enriched natural uranium or uranium-233 as a fuel for a nuclear power reactor. However, this reference does not disclose any processing of protactinium which normally appears in the spent fuel of reactors which utilize the thorium uranium fuel cycle.
Other prior art disclosures which relate to the field of the invention include the following: U.S. Pat. No. 2,954,335 to Wigner, U.S. Pat. No. 2,860,093 to Wigner, U.S. Pat. No. 3,309,277 to Jaye, U.S. Pat. No. 4,018,697 to Smith, British Patent No. 873,171 issued to the United Kingdom Atomic Energy Authority, and the following two monographs: "The Separation of Nuclear Power from Nuclear Proliferation," by Chauncey Starr, presented at the Fifth Energy Technology Conference, Washington, D.C., February 1978; and "Gilinsky Raises Plutonium Retransfer Doubts," Nucleonics Week, Sept. 28, 1978, page 8.
The problem of nuclear fuel proliferation, notably with fuels such as uranium and plutonium, has been a long standing one which has gained wide spread public attention and awareness. Therefore, a significant incentive for adequately coping with this problem exists.